The present invention relates generally to printers, and more particularly to a method for controlling the paper feed of a printer.
Printers include those printers having a paper-feed roller which rotates to a desired rotational position to advance a paper sheet, such as to advance a paper sheet between print swaths printed by a print head mounted on a carrier system. In a known design, a DC (direct current) motor is used to drive the paper-feed roller. An output signal from a paper-feed controller, such as a proportional or a PI (proportional integral) or a PID (proportional integral derivative) controller, is used to control the motor. Typically, the controller is used in a feedback control system wherein an encoder measures the rotational position of the paper-feed roller and wherein the error signal between the actual rotational position (measured by the encoder) and the desired rotational position is used as the input to the controller. In one known mode of operation, once the paper-feed roller reaches the desired rotational position, the controller shuts the motor off. However, in this one mode, the quick release of the trapped energy in the gear train and the motor tends to displace the paper-feed roller away from its desired position. In another known mode of operation, the controller remains active. However, in this other mode, vibrations induced by the carrier system may be amplified by the paper-feed controller.
What is needed is an improved method for rotating a printer paper-feed roller.
A broadly-described expression of a method of the invention is for rotating a printer paper-feed roller toward a desired rotational position wherein the printer paper-feed roller is driven by a motor. The broadly-described expression of a method of the invention includes steps a) and b). Step a) includes controlling the motor with a signal which at least includes the product of a scale factor and a function of an error signal, wherein the error signal represents the difference between the actual rotational position and the desired rotational position of the printer paper-feed roller. Step b) includes varying the scale factor in a predetermined manner over time when a predetermined condition has been met. In one example, the scale factor is decreased in a linear manner over time when the predetermined condition has been met. In one implementation, the predetermined condition is a predetermined rotational distance of the printer paper-feed roller from the desired rotational position. In another implementation, the predetermined condition is a predetermined time which includes the expected time to rotate the printer paper-feed roller to the desired rotational position.
Several benefits and advantages are derived from the broadly-described expression of a method of the invention. In one example, decreasing the scale factor over time gradually releases the trapped energy in the gear train and the motor thereby avoiding the prior art problem of displacing the paper-feed roller away from its desired position when the motor is abruptly shut off. Decreasing the scale factor over time also avoids the prior art problem of the paper-feed controller amplifying vibrations induced by the carrier system when the controller remains active.